Rich-lean combustion burner

ABSTRACT

A row of rich-side flame holes of a combustion burner is arranged in center. Two rows of lean-side flame holes are arranged respectively on sides of the rich-side flame hole row. Two rows of rich-side flame holes are arranged respectively on the outsides of the two lean-side flame hole rows. Supply of lean-side mixture is provided to the lean-side flame hole rows from a tubular part. A lower end part of a central rich-side burner part is projected into a tubular part, into which the rich-side mixture is introduced, to establish lateral fluid communication, with its lower end edge placed in a state of non-contact with the inner surface of the tubular part. First communication holes in fluid communication with an internal space are opened in the lower end part. Communication holes in fluid communication with the outer rich-side flame holes are opened in the inside of the tubular part.

TECHNICAL FIELD

The present invention relates to a rich-lean combustion burner with rich-side flame holes and lean-side flame holes. In particular, this invention relates to technology for accomplishing uniformity of the concentration of and the amount of rich-side mixture for supply to the rich-side flame holes.

BACKGROUND ART

Heretofore, there have been proposed various types of rich-lean combustion burners (see, for example, Patent Literature Publications 1 and 2). In a rich-lean combustion burner of such a type, a lean-side mixture having an air ratio of in excess of 1.0 is burned at lean-side flame holes for the reduction of NOx. And for the stabilization of combustion flames, rich-side flame holes, at which a rich-side mixture having an air ratio of below 1.0 is burned, are arranged adjacent to the lean-side flame holes. According in particular to the proposal of Patent Literature Publication 3, in the case where fuel gas and air are supplied to and mixed together in a mixing chamber for the production of a rich-side mixture, there is formed, on the side of the inner surface of an inlet port of the mixing chamber, a mixing accelerating member (e.g., a member formed by notching or by cutting/lifting).

CITATION LIST Patent Literature

Literatures cited are:

Patent Literature Publication 1: JP-A-H07-42917;

Patent Literature Publication 2: JP-A-2002-48314; and

Patent Literature Publication 3: Japanese Patent No. 3636347

SUMMARY OF INVENTION Technical Problem

Incidentally, as a method for separate supply of a rich-side mixture and a lean-side mixture respectively to rich-side flame holes and to lean-side flame holes, Patent Literature Publication 1 shows one in which a rich-side mixture supply port and a lean-side mixture supply port are separately provided so that a rich-side mixture is directly fed to rich-side flame holes through the rich-side mixture supply port while on the other hand a lean-side mixture is directly fed to lean-side flame holes through the lean-side mixture supply port. In addition, according to Patent Literature Publication 2, a fuel gas supply port and an air supply port are separately provided and the supply channels extending respectively to rich-side flame holes and to lean-side flame holes are branched or varied in length, thereby controlling the level of mixture richness/leanness.

If the rich-lean combustion burner is of the type that rich-side flame holes are arranged on both sides of a single row of lean-side flame holes (that is, the lean-side flame hole row is merely sandwiched from both sides), this allows the supply methods proposed by the aforesaid Patent Literature Publications to provide the supply of rich-side mixture and lean-side mixture. However, if rich-side flame holes and lean-side flame holes are alternately arranged side by side in order of RICH-LEAN-RICH-LEAN-RICH in the lateral direction (i.e., the width direction) by addition of another row of rich-side flame holes extending in the direction of the rich-side flame hole's central line, this may result in causing inconvenience in the supply of rich-side mixture. In other words, when supplying rich-side mixture and lean-side mixture respectively to rich-side flame holes and to lean-side flame holes, the supply of the rich-side mixture to the rich-side flame holes situated at three different positions (i.e., the rich-side flame holes in the center, the rich-side flame holes on the right-hand side and the rich-side flame holes on the left-hand side) becomes inconvenienced. For example, in the case where the flow of rich-side mixture from the mixing chamber is diverged and supplied to the rich-side flame holes in the aforesaid three positions so that the rich-side mixture is distributed to the rich-side flame holes in each position, it is conceivable that the concentration (primary air ratio) of and the amount of rich-side mixture supplied, in particular, to the rich-side flame holes on both horizontal sides are likely to become uneven due to mounting errors with respect to: (i) the relative mounting position of a mixing chamber to a manifold adapted to supply fuel gas to the mixing chamber, (ii) when combining rich-lean combustion burners in a plurality of rows, the relative mounting position of each rich-lean combustion burner to the other, or (iii) the relative mounting position of various components used for partition-formation of portions by which the flow of rich-side mixture from the mixing chamber is diverged to provide the supply thereof For example, referring to FIG. 18, there is shown a structural example for the purpose of comparison. In this example of FIG. 18, the downstream end side (the far side in the direction perpendicular to the drawing) of a tubular-shaped mixing chamber 100 is horizontally divided by a component 102 having a communication hole to central rich-side flame holes 101 into two portions, and communication holes diverged to outer rich-side flame holes 103, 103 are formed respectively in the outer walls thus horizontally divided. On the other hand, there is disposed a fuel gas jet nozzle 105 of the manifold facing in the direction of an opening 104 on the upstream end side (the near side of the drawing) of the mixing chamber 100. In this case, under normal conditions, the jet nozzle 105 should be mounted such that its nozzle central axis and that of the mixing chamber 100 are in coaxial relation to each other. However, if the jet nozzle 105 is horizontally decentered in position relative to the mixing chamber 100 due to mounting errors such as an eccentric positional deviation exaggeratedly shown in FIG. 18 by referential numeral 105′, it is conceivable that the rich-side flame holes 103, 103 on both horizontal sides are likely to become uneven in the concentration (primary air ratio) of and the amount of rich-side mixture.

With these circumstances as described above in mind, the present invention was developed. Accordingly, an object of the present invention is to provide a rich-lean combustion burner capable of providing, by means of a simple configuration and in a reliable manner, the supply of lean-side mixture and rich-side mixture respectively to lean-side flame holes and to rich-side flame holes and in addition, capable of accomplishing uniformity of the concentration of and/or the amount of rich-side mixture supplied to a plurality of rich-side flame holes.

Solution to Problem

To this end, the present invention has the following specific particulars intended for a rich-lean combustion burner in which two rows of lean-side flame holes are disposed so as to sandwich, therebetween and from both lateral sides, one row of central rich-side flame holes disposed so as to longitudinally extend in a central position and two rows of outer rich-side flame holes are disposed so as to sandwich, therebetween and from outside, both the two rows of lean-side flame holes. More specifically, the flow of a rich-side mixture, introduced into a single rich-side mixture introduction channel whose downstream end is a closed end, is diverged so that the rich-side mixture is distributed to the one row of central rich-side flame holes and to the two rows of outer rich-side flame holes, and a first rich-side mixture supply channel for supply of the rich-side mixture to the one row of central rich-side flame holes, a second and a third rich-side mixture supply channel for individual supply of the rich-side mixture to each of the two rows of outer rich-side flame holes and the rich-side mixture introduction channel are partitioned from one another. And a portion of a formation member for partition formation of the first rich-side mixture supply channel is disposed so as to project into the rich-side mixture introduction channel and a first communication hole in fluid communication with the first rich-side mixture supply channel is formed in the projecting portion of the formation member so as to open facing towards the inside of the rich-side mixture introduction channel, and on the other hand, a second communication hole in fluid communication with the second rich-side mixture supply channel and a third communication hole in fluid communication with the third rich-side mixture supply channel are formed in a formation member for partition formation of the rich-side mixture introduction channel such that the second and the third communication holes each open facing towards the inside of the rich-side mixture introduction channel. And the projecting portion is disposed such that its end edge and an inner surface of the rich-side mixture introduction channel are placed in a state of non-contact with each other.

The rich-lean combustion burner of the present invention, whose rows of rich-side and lean-side flame holes are arranged in order of RICH-LEAN-RICH-LEAN-RICH, makes it possible that the flow of rich-side mixture brought in from a single rich-side mixture introduction channel is split into sub-flows so that the rich-side mixture is distributed separately to the row of central rich-side flame holes through the first communication hole of the projecting portion projected into the rich-side mixture introduction channel and to the two rows of outer rich-side flame holes through the second and the third communication holes formed in the formation member for partition formation of the rich-side mixture introduction channel. As a result of this, even for the case of the aforesaid rich-lean combustion burner provided with rich- and lean-side flame holes which are arrayed in rows in order of RICH-LEAN-RICH-LEAN-RICH, it becomes possible to ensure that the flow of rich-side mixture is smoothly and reliably diverged and then supplied to each rich-side flame hole by a simple structure.

Being premised on the advantageous effects as described above, the rich-lean combustion burner according to the present invention further achieves the following advantageous effects. For example, if at the time of assembling a rich-lean combustion burner in a combustion apparatus, there occurs an assembly error regarding the relative positional relationship between the rich-lean combustion burner and a gas manifold, this may possibly cause the condition that the fuel gas ejection nozzle of the gas manifold undergoes an eccentric positional deviation against the rich-side mixture introduction channel. Or if when performing an assembly operation so that the projecting portion is arranged in place and projected into the rich-side mixture introduction channel, there occurs an assembly error, this may possibly cause the condition that the projecting portion undergoes an eccentric positional deviation against the inside of the rich-side mixture introduction channel. Even if there occurs a condition of such type, the rich-lean combustion burner of the present invention, however, prevents the occurrence of inconvenience due to the condition occurred. In other words, the flow of rich-side mixture is diverged so that the rich-side mixture is distributed, at the same primary air ratio as in the case where there occurs no eccentric positional deviation, separately to the second communication hole in fluid communication with the second rich-side mixture supply channel and to the third communication hole in fluid communication with the third rich-side mixture supply channel. And, it becomes possible to produce uniform rich-side flames at the outer rich-side flame holes on both sides which are supplied with rich-side mixture from the second rich-side mixture supply channel and from the third rich-side mixture supply channel, respectively.

That is, if in the case where the projecting portion is projected so as to divide the rich-side mixture introduction channel into two space regions, there occurs an eccentric positional deviation associated with an assembly error as described above, this will easily result in the condition such as an uneven distribution of the rich-side mixture to any one of the two space regions on the closed end side of the rich-side mixture introduction channel or an uneven absorption of the variation in internal pressure. These conditions cause inconvenience as follows: the two outer rich-side flame hole rows each produce rich-side flames differing from the other in their primary air ratio or produce unbalanced rich-side flames due to the occurrence of vertical variation. On the other hand, if the projecting portion is disposed so that its end edge is placed in a state of non-contact with the inner surface of the rich-side mixture introduction channel (as in the rich-lean combustion burner of the present invention), this makes it possible that even when there occurs an eccentric positional deviation as described above, there is established, at that non-contact space portion in the inside of the non-contact region, fluid communication, thereby eliminating uneven distribution of the rich-side mixture and pressure absorption unevenness as described above. Therefore, it is possible that the flow of rich-side mixture is diverged, at a uniform air ratio, both to the second communication hole in fluid communication with the second rich-side mixture supply channel and to the third communication hole in fluid communication with the third rich-side mixture supply channel, even when there occurs, due to an assembly error, an eccentric positional deviation as described above. This enables the rows of outer rich-side flame holes to produce uniform rich-side flames by use of rich-side mixtures of the same air ratio, and in addition, it becomes possible to prevent, without fail, the occurrence of formation of unbalanced rich-side flames due to the occurrence of vertical variation. The above-described functional effects become useful, especially when the rich-side mixture introduction channel is configured so as to serve as a mixing chamber to which upstream end fuel gas and air are separately supplied and in which the fuel gas and the air are mixed together to change to a given rich-side mixture during flow to the closed end as a downstream end.

In the rich-lean combustion burner of the present invention, the projecting portion may be arranged in place so that its lower end edge extending in the upstream and downstream direction of the rich-side mixture introduction channel and an inner bottom surface of the rich-side mixture introduction channel are placed in a state of non-contact with each other. This brings a space portion in the inside of the rich-side mixture introduction channel, which space portion is defined between the lower end edge and the inner bottom surface which are in opposing relationship in vertical direction, into lateral fluid communication. Owing to such arrangement, over the upstream and downstream direction, the space portion vertically defined between the lower end and the inner bottom surface of the rich-side mixture introduction channel is brought into lateral fluid communication, thereby further ensuring that the advantageous effects of the present invention are accomplished.

Alternatively, the projecting portion may be arranged in place so that its end edge facing towards the closed end of the rich-side mixture introduction channel and an inner surface of the closed end are placed in a state of non-contact with each other. This brings a space portion in the inside of the rich-side mixture introduction channel, which space portion is defined between the end edge and the inner surface which are in opposing relationship in upstream and downstream direction, into lateral fluid communication. Owing to such arrangement, the inside of the rich-side mixture introduction channel in the vicinity of the closed end which is the downstream end of the rich-side mixture introduction channel is brought into lateral fluid communication. In addition to this, the aforesaid configuration that the vertical space portion is brought into lateral fluid communication may be additionally employed.

In the rich-lean combustion burner of the present invention, it may be arranged as follows: in the inside of the projecting portion, the first rich-side mixture supply channel is partition-formed between one pair of walls situated facing each other in lateral direction, with a predetermined lateral inner width spaced therebetween; the first communication hole is formed in each of the wall pair; and both the first communication holes are formed so as to pass through in alignment with each other in lateral direction. In this case, since both the first communication holes formed respectively in the one pair of walls are passed therethrough in lateral alignment, thereby being placed in a state of fluid communication with the rich-side mixture introduction channel without any lateral interruption. Because of this, the flow of rich-side mixture flowing towards the rich-side mixture supply channel through each first communication hole from the rich-side mixture introduction channel is allowed to smoothly move into the first supply channel without collision against obstacles such as wall surfaces. This makes it possible to prevent the possibility that dust particles likely of being contained in the air constituting the rich-side mixture will adhere and accumulate after collision against obstacles such as wall surfaces. This prevents the state of combustion from becoming instable due to the adhesion and accumulation of dust particles.

It may be arranged that the first communication hole is formed so as to have an opening the size of which is equal to or in excess of the inner width between the wall pair at a location where the first communication hole is formed. Owing to this arrangement, it becomes possible to more reliably avoid the occurrence of adhesion and accumulation of dust particles. In other words, since not only both the first communication holes are just brought in alignment with each other but also they have a large opening area, this makes it possible to prevent the entire flow of inflowing rich-side mixture from collision against obstacles such as wall surfaces.

Alternatively, it may be arranged that the first communication hole is formed at a position in the projecting portion which position is situated nearer to the upstream of the rich-side mixture introduction channel so that there is left an internal space on the side nearer to the closed end of the rich-side mixture introduction channel than the first communication hole formation location. Owing to this arrangement, even in the case where dust particles are contained in the rich-side mixture in the rich-side mixture introduction channel, the dust particles are held in the internal space downstream of each first communication hole, thereby making it possible to prevent their entrance to the first supply channel from each first communication hole.

Furthermore, it may be arranged that the first communication hole is formed at an upper part of the projecting portion in the rich-side mixture introduction channel. Owing to this arrangement, the first communication hole coincides with the flow of rich-side mixture flowing through the rich-side mixture introduction channel, thereby accomplishing more smooth inflow of the rich-side mixture. To sum up, as the rich-side mixture, introduced into the rich-side mixture introduction channel and then flowing downstream, advances in the downstream direction, the flow thereof changes direction to now travel slightly obliquely upward, thereby making its entry more easy. In addition, even in the case where dust particles, which have entered together with the air forming the rich-side mixture, remain and accumulate in the rich-side mixture introduction channel, the possibility of the first communication holes being clogged is reduced thanks to the arrangement that the first communication holes are each formed at the upper position of the projecting portion in the rich-side mixture introduction channel. Furthermore, even if in the combustion stopped state, airborne dust or the like enters from the rich-side flame holes at the upper end and falls downward in the rich-side mixture supply channel, such dust is collected at a lower position than each communication hole, thereby making it possible to ensure the flowing-in of rich-side mixture through each communication hole without any interruption.

In the rich-lean combustion burner of the present invention, it may be arranged that pluralities of communication holes are provided, in the upstream and downstream direction of the rich-side mixture introduction channel, respectively as the second communication hole in fluid communication with the second rich-side mixture supply channel and as the third communication hole in fluid communication with the third rich-side mixture supply channel and in addition, that of the pluralities of communication holes, ones situated on the upstream side are formed so as to have a larger diameter than the others situated on the downstream side. Owing to this arrangement, the rich-side mixture introduced into the rich-side mixture introduction channel flows, at a uniform flow rate, into the communication holes on the upstream side and into the communication holes on the downstream side. In other words, the rich-side mixture introduced into the rich-side mixture introduction channel is forced in the direction of the closed end which is a downstream end and the internal pressure at a region in the vicinity of the closed end increases, so that the rich-side mixture will flow into the downstream communication holes, situated nearer to the closed end, at a higher flow velocity. On the other hand, the rich-side mixture flows, at a lower flow velocity, into the upstream communication holes situated farther away from the closed end because the inner pressure is relatively lower than at the position of the downstream communication hole. Therefore, the amount of rich-side mixture flowing, via the second or the third rich-side mixture supply channel, into the side of the outer rich-side flame holes from the downstream communication holes having a smaller opening area because of its smaller diameter into which the rich-side mixture flows at a higher flow velocity becomes identical with the amount of rich-side mixture flowing, via the second or the third rich-side mixture supply channel, into the side of the outer rich-side flame holes from the upstream communication holes having a larger opening area into which the rich-side mixture flows at a lower flow velocity. Because of the above, even when the outer rich-side flame holes are formed so as to extend in the longitudinal direction, the flow of rich-side mixture from the upstream communication holes and the flow of rich-side mixture from the downstream communication holes are dispersed to each other in the lateral direction for distribution at a uniform flow rate. In this case, additionally, the end edge of the projecting portion is placed in a state of non-contact with the inner surface of the rich-side mixture introduction channel, that is, the inside of the rich-side mixture introduction channel is not partitioned so as to establish lateral fluid communication therein, whereby even when the second communication hole in fluid communication with the second rich-side mixture supply channel and the third communication hole in fluid communication with the third rich-side mixture supply channel are arranged on both lateral sides, the rich-side mixture is supplied, at a uniform primary air ratio, to these communication holes.

Alternatively, it may be arranged that a plurality of communication holes are provided, in the upstream and downstream direction of the rich-side mixture introduction channel, as the first communication hole wherein one of the plurality of communication holes situated on the upstream side is formed so as to have a larger diameter than the other situated on the downstream side. Owing to this arrangement, the rich-side mixture introduced into the rich-side mixture introduction channel flows, at a uniform flow rate, into the upstream communication holes and into the downstream communication holes. In other words, as described above, the rich-side mixture introduced into the rich-side mixture introduction channel is forced in the direction of the closed end which is a downstream end and the internal pressure at a region in the vicinity of the closed end increases, so that the rich-side mixture will flow into the first communication hole on the downstream side, situated nearer to the closed end, at a higher flow velocity. On the other hand, the rich-side mixture flows, at a lower flow velocity, into the first communication hole on the upstream side situated farther away from the closed end because the inner pressure is relatively lower than at the position of the first communication hole on the downstream side. Therefore, the amount of rich-side mixture flowing, via the first rich-side mixture supply channel, into the side of the central rich-side flame holes from the first communication hole on the downstream side having a smaller opening area because of its smaller diameter into which the rich-side mixture flows at a higher flow velocity becomes identical with the amount of rich-side mixture flowing, via the first rich-side mixture supply channel, into the side of the central rich-side flame holes from the first communication hole on the upstream side having a larger opening area into which the rich-side mixture flows at a lower flow velocity. Because of the above, even when the central rich-side flame holes are formed so as to extend in the longitudinal direction, the flow of rich-side mixture from the first communication hole on the upstream side and the flow of rich-side mixture from the communication hole on the downstream side are dispersed to each other in the lateral direction for distribution at a uniform flow rate.

In addition, it may be arranged that the first communication hole is formed in the shape of a long hole which is elongated in a direction in which the rich-side mixture introduction channel extends. Owing to this arrangement, the first communication hole is formed so as to be elongated in a direction corresponding to the direction in which the rich-side mixture introduction channel extends, i.e., in the direction in which the flow of rich-side mixture moves, whereby the rich-side mixture is more smoothly admitted into the first rich-side mixture supply channel from the rich-side mixture introduction channel through the first communication hole. Because of this, the flow of rich-side mixture flowing into the first rich-side mixture supply channel through both the first communication holes becomes more smooth while preventing, without fail, the occurrence of conditions (such as collision against wall surfaces) that contribute to the adhesion and accumulation of dust particles.

And by providing a combustion apparatus by use of a rich-lean combustion burner as described above, it becomes possible for the combustion apparatus to produce the foregoing various advantageous effects.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings:

FIG. 1, comprised of FIG. 1( a) and FIG. 1( b), shows an example of a combustion apparatus into which a rich-lean combustion burner according to the present invention is incorporated, wherein FIG. 1( a) is an illustration diagram showing a perspective view of the rich-lean combustion burner and FIG. 1( b) is an illustration diagram showing a cross-sectional view of the rich-lean combustion burner;

FIG. 2 is a perspective view of a rich-lean combustion burner according to a first embodiment of the present invention;

FIG. 3 is a front view of the burner of FIG. 2;

FIG. 4 is comprised of FIG. 4( a), FIG. 4( b) and FIG. 4( c), wherein FIG. 4(a) is a top plan view of the burner of FIG. 2, FIG. 4( b) is a partially enlarged view of an H-H part of FIG. 4( a) and FIG. 4( c) is a left-hand side view of the burner of FIG. 2;

FIG. 5 is a perspective view showing, in an exploded manner, a pair of third plate members constituting a central rich-side burner part, a flame hole member constituting rows of lean-side flame holes arranged in place on both sides of the central rich-side burner part, a second plate member and a first plate member;

FIG. 6 is a partial perspective view when cut at a cross section along line A-A of FIG. 3;

FIG. 7 is comprised of FIG. 7( a) and FIG. 7( b), wherein FIG. 7( a) is a perspective view when cut along line B-B of FIG. 3 and FIG. 7( b) is a perspective view when cut along line C-C of FIG. 3;

FIG. 8 is comprised of FIG. 8( a) and FIG. 8( b), wherein FIG. 8( a) is an illustration diagram in cross section taken along line A-A of FIG. 3 and FIG. 8( b) is an illustration diagram showing, in an enlarged manner, a D part of FIG. 8( a);

FIG. 9 is an illustration view illustrating, in the form of a perspective view, a state when cut and exploded in a lateral central position;

FIG. 10 is a partially enlarged cross-sectional illustration view taken along line E-E of FIG. 9;

FIG. 11 is a perspective view showing a third plate member employed in a second embodiment of the present invention and formed in such a way that, as a substitute for a pair of third plate members, a plate member in the form of a single sheet is bent to provide a central rich-side burner;

FIG. 12 is a corresponding diagram to FIG. 8( b) to which the central rich-side burner formed by using the third plate member of the second embodiment is applied;

FIG. 13 is an illustration diagram showing, in the form of a perspective view when cut and exploded in a lateral central position, a state in a third embodiment of the present invention in which two types of communication holes different in size (small and large) are formed in a third plate member;

FIG. 14 is comprised of FIG. 14( a) and FIG. 14( b) wherein FIG. 14( a) is a partially enlarged illustration diagram in cross section taken along line F-F of FIG. 13 and FIG. 14( b) is a corresponding diagram to FIG. 14( a) showing another manner of the third embodiment;

FIG. 15 is a perspective view showing a rich-lean combustion burner according to a fourth embodiment of the present invention;

FIG. 16 is comprised of FIG. 16( a) and FIG. 16( b) wherein FIG. 16( a) is an illustration diagram showing, in the form of a perspective view, the state of a rich-lean combustion burner of a fourth embodiment of the present invention when cut and exploded in a lateral central position as in FIG. 13 and FIG. 16( b) is an illustration diagram in cross section taken along line G-G of FIG. 16( a);

FIG. 17 is comprised of FIG. 17( a) and FIG. 17( b) wherein FIG. 17( a) is a corresponding view to FIG. 9 showing a fifth embodiment of the present invention and FIG. 17( b) is a partial front view of FIG. 17( a);

FIG. 18 is an illustration diagram for explaining problems to be solved by the present invention and is an enlarged, cross-sectional illustration diagram corresponding to FIG. 4( c); and

FIG. 19 is an illustration diagram for explaining other problems to be solved by the present invention and is an enlarged, cross-sectional illustration diagram corresponding to FIG. 8( b).

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, there is shown a combustion apparatus 2 into which rich-lean combustion burners 3, 3, . . . according to each of embodiments of the present invention are incorporated. The combustion apparatus 2 includes a can body 21 inside which a set of burners, made up of a predetermined number of rich-lean combustion burners 3, 3, . . . which are laterally adjacently arranged, is firmly fixed. The upper space of the can body 21 serves as a combustion space 22 and its lower space 23 is supplied with combustion air from an air distribution fan 24 and on the other hand, there is disposed on one side of each rich-lean combustion burner 3 a gas manifold 25 (shown only in FIG. 1( b)), and projected from the gas manifold 25 to its corresponding rich-lean combustion burner 3 are two gas nozzles 26, 27. One of the gas nozzles 26, 27 (the lower one), i.e., the gas nozzle 26, is configured so as to be able to eject fuel gas in the direction of a first supply port 31 of the rich-lean combustion burner 3 while on the other hand the other gas nozzle (the upper one), i.e., the gas nozzle 27, is configured so as to be able to eject fuel gas in the direction of a second supply port 32 of the rich-lean combustion burner 3. And, air from the lower space 23 is forced in from around each of the gas nozzles 26 and 27 by discharge pressure of the air distribution fan 24 so that both fuel gas and air are supplied to the first and the second supply ports 31, 32. In this case, it is arranged such that the diameter of the first supply port 31 is set to be considerably larger than the outer diameter of the nozzle 26 to thereby allow much more air to be forced in. On the other hand, the diameter of the second supply port 32 is set to be slightly larger than the outer diameter of the nozzle 27 to thereby reduce the amount of air to be forced in. In this way as described above, the first supply port 31 supplies, in addition to fuel gas to be supplied, air so that the amount of air greater than the amount of fuel gas is supplied to the inside at a predetermined air ratio of in excess of 1.0. On the other hand, the second supply port 32 likewise supplies, in addition to fuel gas to be supplied, air so that the amount of air smaller than the amount of fuel gas is supplied to the inside at a predetermined air ratio of less than 1.0. In addition, there is disposed a current plate 28 (see FIG. 1( b)) serving as a partition between the lower space 23 and the rich-lean combustion burners 3, 3, . . . and there are opened through the current plate 28 a great number of small bores, whereby the supply of secondary air is provided between the adjoining rich-lean combustion burner 3, 3 through these small bores.

First Embodiment

As shown in FIG. 2 depicting an example of the first embodiment, the rich-lean combustion burner 3 is composed using (i) three different types of plate members each formed of metallic plate material and worked into predetermined shapes by pressing and bending, i.e., a pair of plate members 4, 4, a pair of plate members 5, 5 and a pair of plate members 6, 6 and (ii) a pair of flame hole formation members 7, 7. The three plate member pairs 4, 4, 5, 5, 6, 6 are placed face to face with one another as will be described later and then joined together in sequence so that the rich-lean combustion burner 3 is provided. The rich-lean combustion burner 3 thus provided is so formed as to have a flattened shape as a whole. Here assuming that the horizontal direction in FIG. 3 is the longitudinal direction (the front-back direction) whereas the direction at right angles to the plane of paper of FIG. 3 is the lateral direction (the width direction), the first supply port 31 and the second supply port 32 having a smaller diameter than that of the first supply port 31 are opened respectively at a lower position and at an upper position on one longitudinal side, i.e., on the left-hand side in FIG. 3 (see also FIG. 4( c)), and a plurality of rows of slit-shaped flame holes where combustion flames are produced are formed in the upper end surface so as to extend in the longitudinal direction. Referring to FIG. 2 or to FIGS. 4( a), 4(b), there are shown rows of flame holes including (i) a rich-side flame hole row 33 of narrow width situated in a lateral central position and extending the longitudinal entire length, (ii) two lean-side flame hole rows 34, 34 of relatively wide width respectively situated in positions on both lateral sides of the rich-side flame hole row 33 and extending the entire longitudinal length and (iii) two rich-side flame hole rows 35, 35 of narrow width respectively situated in positions exterior to the lean-side flame hole rows 34, 34 and extending the entire longitudinal length. And, a lean-side mixture, mixed in the inside after being supplied from the first supply port 31, is directed to each of lean-side flame holes 341 of the lean-side flame hole rows 34, 34, whereby lean-side flames are produced using the lean-side mixture thus distributed. On the other hand, a rich-side mixture, mixed in the inside after being supplied from the second supply port 32 is directed to each of rich-side flame holes 331 of the centrally situated rich-side flame hole row 33 and to each of rich-side flame holes 351 of each of the two rich-side flame hole rows 35, 35 respectively situated in both outer positions, whereby rich-side flames are produced using the rich-side mixture thus distributed.

For example, the rich-lean combustion burner 3 as described above is formed as follows. That is, as shown in FIGS. 4( a), 4(b) and FIG. 5, three different types of plate members (i.e., the plate member pair 4, 4, the plate member pair 5, 5 and the plate member pair 6, 6) and a pair of flame hole formation members (i.e., the flame hole formation member pair 7, 7) are used to constitute the rich-lean combustion burner 3. With the pair of the third plate members 6, 6 placed face to face with each other (see FIG. 5), their both sides and lower edge parts are joined together to thereby define, between the inner surfaces, a rich-side mixture supply channel and form a central rich-side burner part 3 a where rich-side flames are produced in the rich-side flame hole row 33 at the upper surface. Next, the pair of the first plate members 4, 4 are placed face to face with each other from both lateral sides, with the central rich-side burner part 3 a sandwiched therebetween and their both sides and lower edge parts are joined together. In doing so, both longitudinal end parts (front and back end parts) of the central rich-side burner part 3 a are sandwichedly held between both longitudinal end parts (front and back end parts) of the first plate member pair 4, 4, thereby ensuring that the central rich-side burner part 3 a becomes firmly fixed within the rich-lean combustion burner 3. And, the lean-side flame hole formation member 7 is placed in each of two upper end openings (one of which is defined between one of the first plate member pair 4, 4 and the central rich-side burner part 3 a and the other of which is defined between the other of the first plate member pair 4, 4 and the central rich-side burner part 3 a). Because of this arrangement, the central rich-side burner part 3 a is enclosed from both lateral sides to thereby form a lean-side burner part 3 b where lean-side flames are produced in the two lean-side flame hole rows 34, 34 at the upper end surface. In the lean-side burner part 3 b, the lean-side mixture from the first supply port 31 is fed, through a supply channel defined between the inner surface of the first plate member 4 and the outer surface of the third plate member 6 of the central rich-side burner part 3 a, to each lean-side flame hole 341 of the lean-side flame hole rows 34, 34. And the second plate member 5 is placed on the outside of each first plate member 4 of the lean-side burner part 3 b and its both ends and each lower edge part are joined to the edge part of each first plate member 4, whereby there is formed an outer rich-side burner part 3 c (see FIG. 2) to which the rich-side mixture is supplied through a supply channel defined between the inner surface of each second plate member 5 and the outer surface of the first plate member 4 opposite thereto so that rich-side flames are produced at the rich-side flame holes 351 of the outer rich-side flame hole rows 35, 35.

Next, referring now to FIGS. 6 through 10, a description will be given regarding a structural portion adapted for the supply of mixtures. In the aforesaid lean-side burner part 3 b, fuel gas and air from the first supply port 31 opened on one side are mixed together to change to a lean-side mixture during transfer to the other side through a tubular part 36 (see dot-line arrows of FIGS. 7, 9). And, the lean-side mixture in the tubular part 36 changes direction at the other side in the tubular part 36 to now flow upward, thereby being supplied, through two internal spaces 37, 37 (see FIG. 6 and FIG. 7( b)) defined by partition formation (dividing) of a space between the first plate member pair 4, 4 by the third plate member pair 6, 6, to the lean-side flame hole rows 34, 34 at the upper end. The tubular part 36 and the internal spaces 37, 37 together form a lean-side mixture supply channel for providing the supply of lean-side mixture to the two lean-side flame hole rows 34, 34 and in addition, the tubular part 36 serves as a mixing chamber and as a lean-side mixture introduction channel for fuel gas and air supplied from the first supply hole 31. The third plate members 6, 6 constitute a formation member for partition formation of a first rich-side mixture supply channel (to be hereinafter described) and the downstream side of the lean-side mixture introduction channel is halved (divided into two parts) by the third plate members 6, 6, whereby two lean-side mixture supply channels, i.e., the internal spaces 37, 37, are defined by partition formation.

In addition, fuel gas and air from the second supply port 32 are mixed with each other to change to a rich-side mixture while being directed through a tubular part 38 (see FIG. 7( a)) to the closed end side situated at the back (rear). The rich-side mixture is supplied to the central rich-side burner part 3 a and to the outer rich-side burner parts 3 c situated respectively on both lateral sides thereof. In other words, the central rich-side burner part 3 a has a lower end part 60 (see FIG. 7( a) and FIGS. 8( a), 8(b)) which is inserted from above into the closed end side of the tubular part 38 and is formed as a projecting portion projecting in midair in the tubular part 38 (see also FIG. 9). First communication holes 61, 61 are formed respectively in the third plate member pair 6, 6 constituting the lower end part 60 and each first communication hole 61 brings the inside of the tubular part 38 and an internal space 62 of the central rich-side burner part 3 a into fluid communication with each other. The internal space 62 constitutes a first rich-side mixture supply channel, and the rich-side mixture in the tubular part 38 is supplied, through each first communication hole 61 and through the first rich-side mixture supply channel, to the rich-side flame hole row 33. On the other hand, second and third communication holes 41, 41 are formed respectively in the first plate member pair 4, 4 constituting the tubular part 38. Through each second communication hole 41 of the first plate member 4 on one lateral side (the right-hand side of FIG. 6, the right-hand side of FIG. 8 or the lower side of FIG. 10), the inside of the tubular part 38 is brought into fluid communication with an internal space 51 defined between the first plate member 4 on one side and the second plate member 5 on the same side. On the other hand, through each third communication hole 41 of the first plate member 4 on the other lateral side (the left-hand side of FIG. 6, the left-hand side of FIG. 8 or the upper side of FIG. 10), the inside of the tubular part 38 is brought into fluid communication with an internal space 52 defined between the first plate member 4 on the other side and the second plate member 5 on the same side. The internal space 51 on the one side constitutes a second rich-side mixture supply channel whereas the internal space 52 on the other side constitutes a third rich-side mixture supply channel. Owing to such arrangement, the rich-side mixture in the tubular part 38 is supplied, through each second communication hole 41 on the one lateral side and through the internal space 51 which is the second rich-side mixture supply channel, to the rich-side flame hole row 35 on one side. Likewise, the rich-side mixture in the tubular part 38 is supplied, through each third communication hole 41 on the other lateral side and through the internal space 52 which is the third rich-side mixture supply channel, to the rich-side flame hole row 35 on the other side.

Here, together with the internal spaces 51, 52, 62, the tubular part 38 constitutes a rich-side mixture supply channel, other than which the tubular part 38 is adapted to serve not only as a mixing chamber for fuel gas and air supplied from the second supply port 32, but also as a rich-side mixture introduction channel. And, the lower end part 60 is just projected such that each first communication hole 61 is brought into fluid communication with the space in the tubular part 38, and the lower end edge of the lower end part 60 and the inner bottom surface of the tubular part 38 are placed in a state of non-contact with each other. Owing to such arrangement, the space vertically defined between the lower end edge of the lower end part 60 and the inner bottom surface of the tubular part 38 is not interrupted by anything in the lateral direction (i.e., the horizontal direction in FIG. 8( b)), thereby being left in a state of lateral fluid communication in the tubular part 38. In addition, the first communication holes 61, 61, and the second and the third communication holes 41, 41, . . . may be formed such that they are opened either in positions where they are situated face to face with each other in the lateral direction or in positions where they are out of alignment from each other in the longitudinal direction as in the present embodiment. In other words, it suffices that the first communication holes 61, 61 are each provided so as to open in a region on the closed end side of the tubular part 38 which constitutes a rich-side mixture introduction channel whereas correspondingly to the closed end side of the tubular part 38 where the first communication holes 61, 61 are opened, the second and the third communication holes 41, 41, . . . are formed so that they open in the same region on the closed end side of the tubular part 38.

In the embodiment as described above, the two lean-side flame hole rows 34, 34 are each sandwiched, from both sides, by either the rich-side flame hole rows 35, 33 or the rich-side flame hole rows 33, 35, whereby each lean-side flame produced in both the lean-side flame hole rows 34, 34 is enclosed from both sides by rich-side flames. In other words, it is possible to make the arrangement of flames in order of RICH-LEAN-RICH-LEAN-RICH in the lateral direction. Owing to such arrangement, even in the case where two lean-side flame hole rows 34, 34 are provided to increase the area of lean-side flame hole row, it is possible to prevent the length of lean-side flames from increasing, whereby the height of the combustion chamber 22 (see FIG. 1) can be held short. And, by increasing the lean-side flame hole area (ratio) while holding the height of the combustion chamber short, further NOx reduction and further stabilized combustion are achieved. In addition, as compared to the case where a single rich-lean combustion burner is configured by sandwiching of a single row of lean-side flame holes between rows of rich-side flame holes from both sides, it becomes possible to efficiently achieve better weight saving of the burner in realizing the same lean-side flame hole area. Furthermore, the flow of rich-side mixture, mixed after introduction into the tubular part 38 from a single fuel gas/air supply port (i.e., the second supply port 32), is diverged so that the rich-side mixture is distributed, via the communication holes (namely, the first communication holes 61, 61 of the central rich-side burner part 3 a, the second communication holes 41, 41 of the outer rich-side burner part 3 c and the third communication holes 41, 41 of the outer rich-side burner part 3 c) which are opened in fluid communication with the region on the side of the closed end of the tubular part 38, to their corresponding internal spaces 62, 51, 52, i.e., the first rich-side mixture supply channel, the second rich-side mixture supply channel and the third rich-side mixture supply channel. Owing to such arrangement, even in the case where the three rich-side flame hole rows 35, 33, 35 are provided respectively in the center, on one outside and the other outside, the flow of rich-side mixture can be smoothly and reliably diverged by a simple structure into sub-flows for the supply of rich-side mixture to the rich-side flame hole rows 35, 33, 35.

Furthermore, the following special effects can be achieved. For example, it is conceivable that the jet nozzle 27 may slightly deviate from the lateral central position with respect to the second supply port 32 because of an assembly error occurring when mounting a predetermined number of rich-lean combustion burners 3, 3, . . . (see FIG. 1) into the can body 21 or because of the occurrence of an assembly error regarding the horizontal mount position of the jet nozzle 27 of the manifold 25 (see FIG. 1) with respect to the rich-lean combustion burner 3. In addition, it is conceivable that the lower end part 60 of the third plate members 6, 6 may slightly deviate from the lateral central position with the respect to the inside of the tubular part 38 because of an assembly error occurring at the time of mounting of the third plate member pair 6,6 and the first plate member pair 4, 4. However, even when such an eccentric position deviation occurs, it is possible to produce uniform rich-side flames by diverging and supplying the flow of rich-side mixture having the same air ratio as the case where there occurs no such deviation, to the rich-side flame holes situated on both lateral sides. Here, a comparison will be made regarding the case where, for example, the lower end part 60 of the third plate members 6, 6 is projected up to the inner bottom surface of the tubular part 38 so that the space in the region on the closed end side of the tubular part 38 is laterally partition-formed into two parts wherein the second communication holes 41, 41 in fluid communication with the internal space 51 are formed to open to one of the two partitioned parts while the third communication holes 41, 41 in fluid communication with the internal space 52 are formed to open to the other partitioned part. In this case, if there occurs an eccentric positional deviation due to an assembly error as described above, the amount of fuel gas to be ejected to one of the two partitioned regions on the closed end side of the tubular part 38 differs from that to be ejected to the other partitioned region or there is produced difference between the regions in their volume. Therefore, the air ratio (the primary air ratio) of mixture diverged to the second communication holes 41, 41 situated on one lateral side and the air ratio of mixture diverged to the third communication holes 41, 41 situated on the other lateral side tend to differ from each other, thereby producing the possibility that the rich-side flame hole rows 35, 35 on both outer sides may be supplied with respective rich-side mixtures of different concentrations. In other words, the inside of the tubular part 38 serves as a mixing chamber in which to mix fuel gas and air both supplied through the second supply port 32, and originally, it is expected that the flow of rich-side mixture after proper mixing in the region on the closed end side of the tubular part 38 is diverged to be distributed to the second communication holes 41, 41 on one side and to the third communication holes 41, 41 on the other side.

However, if the amount of fuel gas ejected to one of the two partitioned regions on the closed end side differs from that of the other partitioned region, or if each region differs from the other in their volume, this tends to cause conditions such as uneven distribution of gas and air to any one of the regions and uneven absorption of the variation in pressure in the tubular part 38 serving as a mixing chamber. These conditions cause inconvenience. That is, the rich-side flame hole rows 35, 35 on both sides produce rich-side flames at different primary air ratios and there occurs a vertical variation to produce unbalanced rich-side flames. On the other hand, as in the present embodiment, the projection position of the lower end edge of the lower end part 60 is set such that it is projected to a vertical intermediate position in the tubular part 38. In other words, the lower end edge of the lower end part 60 and the internal bottom surface of the tubular part 38 is placed in non-contact relation with each other so that the inside of the tubular part 38 vertically defined therebetween remains in lateral fluid communication, whereby it becomes possible that even in the region situated on the closed end side, the lower side region within the tubular part 38 is placed in lateral fluid communication without any lateral interruption. Therefore, even when the aforesaid eccentric positional deviation occurs due to an assembly error, there is no possibility that, as a result of the difference between the air ratio (primary air ratio) of mixture the flow of which is diverged to the second communication holes 41, 41 situated on one lateral side and the air ratio of mixture the flow of which is diverged to the third communication holes 41, 41 situated on the other lateral side, the concentration of rich-side mixture supplied to one of the rich-side flame hole rows 35, 35 situated respectively on both outer sides will differ from the concentration of rich-side mixture supplied to the other of the rich-side flame hole rows 35, 35. Therefore, it becomes possible that the flow of rich-side mixture is diverged, at a uniform air ratio, both to the second communication holes 41, 41 situated on the one lateral side and to the third communication holes 41, 41 situated on the other lateral side. This enables the rich-side flame hole rows 35, 35 situated respectively on both outer sides to produce uniform rich-side flames by use of rich-side mixture of the same air ratio, and in addition, it becomes possible to prevent, without fail, the occurrence of production of unbalanced rich-side flames due to the occurrence of vertical variation.

In addition, the following advantageous effects are provided by the first communication holes 61, 61. In other words, the first communication holes 61, 61 are formed so as to pass through the third plate member pair 6, 6 joined together face to face, and in addition, the first communication holes 61, 61 are disposed in place so as to pass through the third plate member pair 6, 6 substantially in lateral alignment with each other (see, for example, FIG. 8( b) and FIG. 10). Stated in another way, although the third plate members 6, 6 are positioned such that their wall surfaces face laterally towards the mixing chamber in the tubular part 38, both the first communication holes 61, 61 are placed in a state of fluid communication with the rich-side mixture introduction channel formed by the tubular part 38 without any interruption in the lateral direction (the vertical direction in FIG. 10) because the first communication holes 61, 61 formed respectively in the third plate members 6, 6 are passed therethrough in alignment. This enables the flow of rich-side mixture moving in the direction of the internal space 62 serving as the first rich-side mixture supply channel from the tubular part 38 via each first communication hole 61 to smoothly flow into the internal space 62 without collision against wall surfaces such as a facing wall 205 or the like in the structural example of FIG. 19. As a result of such arrangement, even when dust particles are contained in the air constituting the rich-side mixture, it is still possible to prevent the occurrence of inconvenience resulting from adhesion and accumulation of the dust particles after collision against obstacles such as wall surfaces. Here, since the point is to avoid the occurrence of adhesion and accumulation of dust particles due to collision against wall surfaces, it is not required that the communication holes 61, 61 are passed through the third plate members 6, 6 in exact alignment with each other, that is, it suffices that the communication holes 61, 61 are more or less in alignment with each other and in addition, there is no need that the communication holes 61, 61 precisely coincide with each other in their lateral orientation and therefore, it suffices if the communication holes 61, 61 are approximately laterally oriented, being opened face to face with each other.

It should be noted here that a structural example shown in FIG. 19 is exemplarily shown only for the purpose of comparison. The structural example of FIG. 19 is one in which the flow of rich-side mixture is diverged from a mixing chamber 200 into sub-flows to rich-side mixture supply channels 201, 201, 203 in fluid communication with rich-side flame holes in three positions (i.e., in the center, on the right-hand side and the left-hand side), whereby the supply of rich-side mixture is provided to the rich-side flame holes situated in the three positions. In this case, it is conceivable that, if the flow of rich-side mixture, admitted from a first communication hole 204 which is adapted for the supply thereof to the rich-side mixture supply channel 201, in particular, to the rich-side flame holes in the central position, collides against the facing wall 205 to the first communication hole 204 as a wall surface constituting the rich-side mixture supply channel 201, this may cause such a condition that dust particles will adhere to and accumulate on the rich-side mixture supply channel 201, as a result of which the passage cross-sectional area of the supply channel 201 is narrowed by the dust particles thus adhered and accumulated. To sum up, the adhesion of airborne dust particles impedes the entrance of the flow of rich-side mixture, therefore making ignition failure and unstable combustion likely to happen. The structure of the first communication holes 61, 61 is capable of preventing such an inconvenience from occurring.

In addition, the diameter of opening of each first communication hole 61 is set so as to be equal to or larger than the inner width, P, of the internal space 62 (the wall space between the pair of the third plate members 6, 6) at the position where the first communication holes 61, 61 are formed (see FIG. 8( b) and FIG. 10). As a result of such arrangement, not only both the communication holes 61, 61 are passed through the third plate members 6, 6 in alignment with each other and in addition, but also the entire flow of inflowing rich-side mixture is prevented from collision against obstacles such as wall surfaces, thereby further ensuring that the occurrence of adhesion and accumulation of dust particles is avoided. In the light of this, each first communication hole 61 may be preferably formed such that the amount of opening (the diameter of opening) is made as large as possible, provided that the setting of the amount of opening, required according to the adjustment or control of of the supply of rich-side mixture to the central rich-side flame holes, is satisfied.

Furthermore, as shown in, for example, FIG. 8( b), each first communication hole 61 may be formed so as to open at a position (an upper position) nearer to the upper portion of the space of the tubular part 38 (the rich-side mixture introduction channel). In other words, each first communication hole 61 is formed so as to open above the portion of the lower end part 60 projecting into the tubular part 38. The reason for this is as follows. The rich-side mixture, moving backward towards the closed end 381 at the rear end from the second supply port 32 at the front end in the tubular part 38, flows slightly obliquely upward as it advances deep inside of the tubular part 38 and, therefore, the position where each first communication hole 61 is formed is set so as to allow the rich-side mixture to more easily flow into each first communication hole 61. In addition, each first communication hole 61 is opened in the vicinity of the upper portion of the tubular part 38 serving as a rich-side mixture introduction channel and therefore, even when dust particles entering along with the air constituting the rich-side mixture remain to accumulate in the rich-side mixture introduction channel, it is possible to prevent the possibility that each first communication hole 61 becomes closed. Further, this means that even when airborne dust or the like enters from each opening of the rich-side flame hole row 33 at the upper end and then falls downward through the internal space 62, such dust will be collected in a lower position than each communication hole 61 of the lower end part 60, thereby contributing to securing the flowing-in of rich-side mixture without preventing the flowing-in of rich-side mixture through each communication hole 61. In addition, each of the communication holes 61, 61 is arranged at a position situated further nearer to the front (a position situated nearer to the upstream) in the range of the rear half part (the downstream side part) of the tubular part 38 (the rich-side mixture introduction channel) extending, in the front-back direction, from the second supply port 32 up to the closed end 381. That is, in the inside of the tubular part 38 situated on the side rearward of each communication hole 61 and extending up to the closed end 381, there is left an internal space serving as a pocket part 382 (see FIG. 10) for collection of dust particles. Because of this, even when the rich-side mixture present in the tubular part 38 contains dust particles, the dust particles are collected in the internal space of the pocket part 382, to thereby prevent the dust particles from flowing into the internal space 62 from each communication hole 61.

The following setting will suffice in order that the rich-side mixture can be distributed, at the same flow rate and pressure, to the rich-side flame hole row 35 on one side in fluid communication with the internal space 51 which is the second rich-side mixture supply channel, to the rich-side flame hole row 35 on the other side in fluid communication with the internal space 52 which is the third rich-side mixture supply channel and to the central rich-side flame hole row 33 in fluid communication with the internal space 62 which is the first rich-side mixture supply channel. For example, it may be arranged such that the rich-side flame hole row 35 on one side, the rich-side flame hole row 35 on the other side and the rich-side flame hole row 33 are formed so as to have the same opening area while on the other hand the second communication holes 41, 41 on one side, the third communication holes 41, 41 on the other side and the first communication holes 61, 61 all in fluid communication with the tubular part 38 are formed so as to be identical with each other in their total opening area. In this case, for example, it suffices that it is set such that the second communication hole 41, the third communication hole 41 and the first communication hole 61 are identical in opening area and in number of how many communication holes are formed. For example, on one hand, the number of first communication holes 61 in fluid communication with the internal space 62 is set to two and on the other hand, both the number of communication holes 41 in fluid communication with the internal space 51 and the number of communication holes 41 in fluid communication with the internal space 52 are set to two. Owing to the aforesaid setting made on the opening area of the first communication hole 61, the second communication hole 41, the third communication hole 41 and each rich-side flame hole row 35, 33, it becomes possible that the supply of rich-side mixture is provided at the same flow rate, flow velocity and pressure and in addition, at the same air ratio.

Second Embodiment

Referring to FIG. 11, there is shown a third plate member 6 a employed in a rich-lean combustion burner 3 according to a second embodiment of the present invention. The second embodiment differs from the first embodiment only in employing, as a substitute for the pair of the third plate members 6, 6 used in the first embodiment, a plate member in the form of a single sheet formed by uniting together the third plate member pair 6, 6 (i.e., the third plate member 6 a) and other configurations of this example are the same as those already described in the first embodiment. Therefore, hereinafter, a description will be given mainly in regard to the third plate member 6 a different from its counterpart of the first embodiment and any overlapping description in regard to the other configurations is omitted here.

The third plate member 6 a of the present embodiment is formed using a plate material in the form of a single sheet. In the plate material, plate parts 65, 65 are located respectively on both sides in axisymmetric arrangement across a fold line T extending through the center of the third plate member 6 a. Each plate part 65 is formed, for example, by press so as to have the same shape as that of the third plate 6 in the form of a single sheet in the first embodiment, and both the plate parts 65, 65 are formed such that both of their concave portions are oriented in the same direction (in the upward direction in the example shown in the figure). And, the plate parts 65, 65 on both sides are bent along the fold line T serving as a center so as to be oriented inward (in the direction of an arrow indicated by chain line) to face each other, and their side edges are joined together. This forms the central rich-side burner part 3 a in which a rich-side flame hole row 33 opens upward and both the other end edges and the side of a lower edge are closed.

In this way described above, the rich-lean combustion burner 3 is formed using the third plate member 6 a. Therefore, as shown in FIG. 12, the lower end edge side of the central rich-side burner part 3 a becomes a portion at which the fold line T is set, whereby the lower end edge side of the lower end part 60 of the central rich-side burner part 3 a is completely closed, and in addition, joint operations can be omitted accordingly. This ensures that leakage due to joint errors or the like in the lower end part 60 and the possibility of the occurrence of inflow between the inside and the outside of the internal space 62 are prevented. In addition, the portion where the fold line T is set is extended in a straight line throughout the entire longitudinal length of the central rich-side burner part 3 a. In other words, the portion is formed into a straight shape, whereby the lower end part 60 of the central rich-side burner part 3 a is formed into a straight shape extending in a straight line throughout the entire longitudinal length of the central rich-side burner part 3 a, as shown in FIG. 13. Although the lower end part 60 becomes exposed not only within the tubular part 38 but also in the bend portion on the rear side of the tubular pat 36, it is possible to prevent and avoid, without fail, the flowing-in of lean-side mixture in the tubular part 36 into the central rich-side burner part 3 a and the occurrence of leakage of rich-side mixture from within the central rich-side burner part 3 a into the tubular part 36.

In addition, in the present embodiment, the description has been given regarding an example case where instead of using the third plate members 6, 6 of the different plate member pairs 4, 4, 5, 5 and 6, 6 employed in the first embodiment, the rich-lean combustion burner 3 is formed by use of a plate member in the form of a single sheet (the third plate member 6 a); however, this should not be considered as a limitation. That is, it may be arranged that instead of joining and mounting another pair of plate members, the rich-lean combustion burner 3 is formed by bending a plate member in the form of a single sheet, as in the above. In addition, for example, the ends of plate members differing from each other in shape and type (e.g., the second plate member 5 and the third plate member 6) are made continuous with each other to form a single member which is then bent to form a rich-lean combustion burner 3. Thus, the method of forming the rich-lean combustion burner 3 is not limited to those as set forth in each embodiment of the present invention.

Third Embodiment

Referring to FIG. 13, there is shown a third embodiment of the present invention. In the third embodiment, a plurality of communication holes are provided so as to open to the inside of the tubular part 38 serving not only as a rich-side mixture mixing chamber but also as a rich-side mixture introduction channel, and the communication hole diameter is set such that one on the upstream side (on the side of the second supply port 32 of the tubular part 38) has a greater diameter while on the other hand the other on the downstream side has a smaller diameter. Other configurations other than this are the same as the first embodiment or the second embodiment and, thus, the configurations represented in the figures are assigned the same signs as in the first and the second embodiments and any overlapping detailed description is omitted and only different points will be described below. In addition, shaded portions in FIG. 13 indicate portions to which the third plate member 6, the plate part 65 and the first plate member 4 (not shown) situated on the other side are joined.

In the present embodiment, a first communication hole 61 a (61) on the upstream side and a first communication hole 61 b (61) on the downstream side, both of which are opened so as to face the inside of the tubular part 38 in the lower end part 60 of the central rich-side burner part 3 a, have a larger diameter and a smaller diameter, respectively. That is, as the first communication hole 61, a plurality of communication holes are formed in the upstream and downstream direction. And, of these communication holes, the first communication hole 61 a on the upstream side is formed so as to have a diameter greater, by a predetermined amount of length, than that of the first communication hole 61 b on the downstream side. This makes it possible that the rich-side mixture as a result of mixing of fuel gas and air supplied to the tubular part 38 flows, at a uniform flow rate, into the first communication hole 61 a on the upstream side and into the first communication hole 61 b on the downstream side. Therefore, it becomes possible that both the rich-side mixture from the first communication hole 61 a on the upstream side and the rich-side mixture from the first communication hole 61 b on the downstream side are dispersed each other in the longitudinal direction and then supplied, at a uniform flow rate, to the rich-side flame hole row 33 extending in the longitudinal direction.

More specifically, since fuel gas and air supplied from the second supply port 32 are forced into the tubular part 38 in the direction of the closed end 381 (see FIG. 14( a)), the internal pressure in the vicinity of the closed end 381 of the tubular part 38 becomes high and therefore, the rich-side mixture will flow into the first communication hole 61 b on the downstream side, situated nearer to the closed end 381 of the tubular part 38 than the first communication hole 61 a, at a higher flow velocity. On the other hand, the first communication hole 61 a on the upstream side situated farther away from the closed end 381 has a lower inner pressure than at the position of the first communication hole 61 b on the downstream side and in addition, the first communication hole 61 a has an opening orthogonal to the flow of rich-side mixture moving in the direction of the closed end 381, whereby the rich-side mixture flows into the first communication hole 61 b at a lower flow velocity. Therefore, the inflow amount of rich-side mixture flowing from the first communication hole 61 b on the downstream side (whose opening area is small and into which the rich-side mixture flows at a higher flow velocity) into the internal space 62 on the side of the rich-side flame hole row 33 becomes identical with the inflow amount of rich-side mixture flowing from the first communication hole 61 a on the upstream stream side (whose opening area is large and into which the rich-side mixture flows at a lower flow velocity) into the internal space 62 on the side of the rich-side flame hole row 33. As a result, even for the case of the rich-lean combustion burner 3 in which the rich-side flame hole row 33 extends in the longitudinal direction so that the rich-lean combustion burner 3 is formed into a flattened shape as a whole, the supply of rich-side mixture to the rich-side flame hole row 33 is provided, with the rich-side mixture uniformly dispersed over the longitudinal direction.

The aforesaid embodiment is directed to the first communication holes 61, 61 of the central rich-side burner part 3 a; however, this should not be considered as a limitation. The embodiment may be directed to the second communication holes 41, 41 and the third communication holes 41, 41 of the outer rich-side burner part 3 c. That is, as exemplarily shown in FIG. 14( b), it is arranged that the second and the third communication holes 41 a (41) on the upstream side which are opened so as to face the inside of the tubular part 38 have a greater diameter while the second and the third communication holes 41 b (41) on the downstream side have a smaller diameter. In other words, as the second and the third communication holes 41, a plurality of communication holes are formed in the upstream and downstream direction. And, of these communication holes, the second and the third communication holes 41 a provided on the upstream side are formed so as to have a bore diameter larger, by a predetermined amount of length, than that of the second and the third communication holes 41 b provided on the downstream side. This arrangement makes it possible that the rich-side mixture as a result of mixing of fuel gas and air supplied to the tubular 38 flows, at a uniform flow rate, both into the second and the third communication holes 41 a on the upstream side and into the second and the third communication holes 41 b on the downstream side. Therefore, it becomes possible that both the rich-side mixture from the second and the third communication holes 41 a on the upstream side and the rich-side mixture from the second and the third communication holes 41 b on the downstream side are dispersed each other in the longitudinal direction and then supplied, at a uniform flow rate, to the rich-side flame hole row 35 extending in the longitudinal direction, and it also becomes possible that in the lateral direction, the rich-side mixture is supplied, at a uniform concentration (at a uniform primary air ratio), both to the second communication holes 41 (41 a, 41 b) on one side and to the third communication holes 41 (41 a, 41 b) on the other side, as described in the first embodiment.

Alternatively, of course, it may be arranged that one and the other one of the first communication holes 61, 61 of the central rich-side burner part 3 a, which are situated respectively upstream and downstream in the upstream and downstream direction, have a greater diameter and a smaller diameter, respectively. And, it may additionally be arranged that ones and the other ones of the second and the third communication holes 41, 41 and 41, 41 of the outer rich-side burner part 3 c, which are situated respectively upstream and downstream in the upstream and downstream direction, have a greater diameter and a smaller diameter, respectively. In this case, it becomes possible that the rich-side mixture is dispersed each other in the longitudinal direction and then supplied, at a uniform flow rate, to each of the rich-side flame hole rows 33, 35, 35 of the central rich-side burner part 3 a and the outer rich-side burner part 3 c.

Fourth Embodiment

Referring to FIGS. 15 and 16, there is shown a rich-lean combustion burner 3 according to a fourth embodiment of the present invention. In the rich-lean combustion burner 3 of the fourth embodiment, the region on the side of the closed end of the tubular part 38 is partitioned by the lower end part 60 of the central rich-side burner part 3 a into two sub-regions laterally, and meanwhile the portion in the vicinity of the closed end of the tubular part 38 is not partitioned whereby the inside of the tubular part 38 is left in a state of lateral fluid communication. To sum up, in each of the first to the third embodiments, the lower end part 60 of the central rich-side burner part 3 a is projected such that it is put in midair in the inside of the tubular part 38, whereby the inside of the tubular part 38 defined vertically between the lower end edge of the lower end part 60 and the internal bottom surface of the tubular part 38 is placed in a state of lateral fluid communication. In the fourth embodiment, on the other hand, the inside of the tubular part 38 defined, relative to the upstream and downstream direction, between the closed end of the tubular part 38 and the end edge on the side of the closed end of the lower end part 60 is placed in a state of lateral fluid communication. Other configurations other than this are the same as in the first embodiment and the configurations represented in the figures are assigned the same signs as in the first embodiment and any overlapping detailed description is omitted and only different points will be described below. In addition, shaded portions in FIG. 16( a) indicate portions to which the third plate member 6 and the first plate member 4 (not shown) on the other side are joined, as in FIGS. 9 and 13.

In the fourth embodiment, as the central rich-side burner part 3 a formed by joining together the third plate members 6, 6, there is provided one that has a lower end part 60 (see FIG. 16) having a projecting portion projecting downward into a convex shape. This lower end part 60 is projected into a region on the side of the closed end 381 in the inside of the tubular part 38 whereby the region of the tubular part 38 is partitioned vertically. More specifically, the region in the tubular part 38 on the side of the closed end 381 is completely divided, in lateral direction, into two sub-regions. On the other hand, as to a region in the vicinity of the closed end 381, the lower end part 60 is left not to project thereinto, thereby placing the end edge of the lower end part 60 facing in the direction of the closed end 381 and the inner surface of the closed end 381 in a state of non-contact with each other, thereby brining a space portion defined between the end edge and the inner surface which are in opposing relationship in vertical direction, into lateral fluid communication. Because of such arrangement, even if there occurs an eccentric positional deviation in lateral direction due to the occurrence of an assembly error as described in the first embodiment, it is still possible that as in the first embodiment, the flow of rich-side mixture having the same air ratio as in the case where there occurs no eccentric positional deviation is diverged and then distributed to both the rich-side flame hole rows 35, 35 situated on the lateral sides respectively, thereby enabling the rich-side flame hole rows 35, 35 to produce uniform rich-side flames.

Here, there is made a comparison to the case where, for example, the space in the closed end side region in the tubular part 38 is laterally divided, all thereover up to the closed end, into two sub-spaces by the lower end part 60 of the third plate members 6, 6. If, in such a case, there occurs an eccentric positional deviation due to the aforesaid assembly error, this may result in causing the amount of fuel gas ejected to one of the two divided sub-spaces of the tubular part 38 on the closed end side to differ from that of the other sub-space or may result in causing these two sub-spaces to differ from each other in their volume. This tends to cause conditions such as uneven distribution of gas and air supplied from the second supply port 32 to any one of the sub-spaces and uneven absorption of the variation in pressure in the tubular part 38 serving as a mixing chamber. These conditions cause inconvenience. That is, the rich-side flame hole rows 35, 35 on both sides produce rich-side flames at different primary air ratios and there occurs a vertical variation to produce unbalanced rich-side flames. On the other hand, according to the present embodiment: (i) some part of the region in the tubular part 38 on the side of the closed end is completely laterally divided, by the lower end part 60, into two sub-regions; (ii) with respect to the inside of the tubular part 38 in the region in the vicinity of the closed end 381, the lower end part 60 is left not to project thereinto and (iii) with the downstream end edge of the lower end part 60 and the inner surface of the closed end 381 brought into a state of non-contact with each other, the inside of the tubular part 38 therebetween is placed in lateral fluid communication, whereby the aforesaid inconveniences are prevented from occurring. Therefore, even when the assembly error causes an eccentric positional deviation, there is no possibility of causing such a condition that the air ratio (primary air ratio) of mixture diverged to the communication holes 41, 41 situated on one lateral side and the air ratio of mixture diverged to the communication holes 41, 41 situated on the other lateral side differ from each other to consequently cause the concentration of rich-side mixture supplied to one of the rich-side flame hole rows 35, 35 and the concentration of rich-side mixture supplied to the other of the rich-side flame hole rows 35, 35 to differ from each other. And, the flow of rich-side mixture is diverged, at a uniform air ratio, both to the second communication holes 41, 41 situated on one lateral side and to the third communication holes 41, 41 situated on the other lateral side. This enables both of the rich-side flame hole rows 35, 35 to produce uniform rich-side flames by use of rich-side mixture of the same air ratio, and in addition, it becomes possible to prevent, without fail, the occurrence of formation of unbalanced rich-side flames due to the occurrence of vertical variation.

Fifth Embodiment

FIG. 17 shows a fifth embodiment of the present invention. This fifth embodiment differs from the first embodiment only in that there is formed a first communication hole 61 a in the shape of a long hole, and all other configurations are the same as their counterparts in the first embodiments. Therefore, hereinafter, a description will be given mainly in regard to different points from the first embodiment and any overlapping description in regard to the other configurations is omitted here.

The first communication hole 61 a of the present embodiment is formed not into a circular shape but into a long hole shape elongated in the longitudinal direction, i.e., in the front-back direction. The position where the first communication holes 61 a, 61 a are formed is the same as that as described in the first embodiment; that is, (i) they pass through side by side in alignment, (ii) they are formed at positions nearer to the upper part of the lower end part 60 and (iii) they are formed at positions nearer to the upstream side or nearer to the front for a pocket part 382 to exist on the downstream side at the rear. In addition, it may be arranged that the longitudinal length of the long hole shape of the communication hole 61 a is made larger than at least the inner width P in the first embodiment.

By employing the first communication holes 61 a, 61 a, the flow of rich-side mixture flowing from the tubular part 38 into the internal space 62 which is the first rich-side mixture supply channel via both of the first communication holes 61 a, 61 a is made more smooth than the first embodiment, while ensuring that the occurrence of conditions, such as collision against the wall surface, that contribute to the adhesion and accumulation of dust particles is avoided. That is to say, since each first communication hole 61 a is formed so as to elongate in the direction in which the tubular part 38 serving as a rich-side mixture introduction channel extends (i.e., in the direction that coincides with the direction of the flow of rich-side mixture). In other words, since each first communication hole 61 a is formed so as to elongate along the flow of rich-side mixture, this enables the rich-side mixture to smoothly flow into the internal space 62 from the tubular part 38. In addition, as a concrete shape available for the long hole, it suffices to employ a long circular shape or an elliptic shape.

Other Embodiments

In each of the first, the second, the fourth and the fifth embodiments, there is shown an example in which there is formed on each lateral side a single communication hole 61 or 61 a, which arrangement, however, should not be considered as a limitation. For example, a plurality of communication holes (two or three communication holes) are formed, being longitudinally arranged side by side. In addition, any one of the first, the second and the third communication holes in the first to the fourth embodiments may be shaped like a long hole as in the fifth embodiment. 

1. A rich-lean combustion burner in which two rows of lean-side flame holes are disposed so as to sandwich, therebetween and from both lateral sides, one row of central rich-side flame holes disposed so as to longitudinally extend in a central position and two rows of outer rich-side flame holes are disposed so as to sandwich, therebetween and from outside, both said two rows of lean-side flame holes, wherein it is arranged that the flow of a rich-side mixture introduced into a single rich-side mixture introduction channel whose downstream end is a closed end is diverged so that said rich-side mixture is distributed to said one row of central rich-side flame holes and to said two rows of outer rich-side flame holes, wherein a first rich-side mixture supply channel for supply of said rich-side mixture to said one row of central rich-side flame holes, a second and a third rich-side mixture supply channel for individual supply of said rich-side mixture to each of said two rows of outer rich-side flame holes and said rich-side mixture introduction channel are partitioned from one another, wherein a portion of a formation member for partition formation of said first rich-side mixture supply channel is disposed so as to project into said rich-side mixture introduction channel and wherein a first communication hole in fluid communication with said first rich-side mixture supply channel is formed in said projecting portion of said formation member so as to open facing towards the inside of said rich-side mixture introduction channel, wherein a second communication hole in fluid communication with said second rich-side mixture supply channel and a third communication hole in fluid communication with said third rich-side mixture supply channel are formed in a formation member for partition formation of said rich-side mixture introduction channel such that said second and said third communication holes each open facing towards the inside of said rich-side mixture introduction channel, and wherein said projecting portion is disposed such that its end edge and an inner surface of said rich-side mixture introduction channel are placed in a state of non-contact with each other.
 2. The rich-lean combustion burner as set forth in claim 1, wherein said projecting portion is disposed such that its lower end edge extending in the upstream and downstream direction of said rich-side mixture introduction channel and an inner bottom surface of said rich-side mixture introduction channel are placed in a state of non-contact with each other, thereby bringing a space portion in the inside of said rich-side mixture introduction channel, which space portion is defined between said lower end edge and said inner bottom surface which are in opposing relationship in vertical direction, into lateral fluid communication.
 3. The rich-lean combustion burner as set forth in claim 1, wherein said projecting portion is disposed such that its end edge facing towards said closed end of said rich-side mixture introduction channel and an inner surface of said closed end are placed in a state of non-contact with each other, thereby bringing a space portion in the inside of said rich-side mixture introduction channel, which space portion is defined between said end edge and said inner surface which are in opposing relationship in upstream and downstream direction, into lateral fluid communication.
 4. The rich-lean combustion burner as set forth in claim 1, wherein in the inside of said projecting portion, said first rich-side mixture supply channel is partition-formed between one pair of walls situated facing each other in lateral direction, with a predetermined lateral inner width spaced therebetween, and wherein said first communication hole is formed in each of said wall pair and wherein both said first communication holes are formed so as to pass through in alignment with each other in lateral direction.
 5. The rich-lean combustion burner as set forth in claim 4, wherein said first communication hole is formed so as to have an opening the size of which is equal to or in excess of said inner width between said wall pair at a location where said first communication hole is formed.
 6. The rich-lean combustion burner as set forth in claim 1, wherein said first communication hole is formed at a position in said projecting portion which position is situated nearer to the upstream of said rich-side mixture introduction channel, thereby leaving an internal space on the side nearer to the closed end of said rich-side mixture introduction channel than said first communication hole formation location.
 7. The rich-lean combustion burner as set forth in claim 1, wherein said first communication hole is formed at an upper part of said projecting portion in said rich-side mixture introduction channel.
 8. The rich-lean combustion burner as set forth in claim 1, wherein pluralities of communication holes are provided, in the upstream and downstream direction of said rich-side mixture introduction channel, respectively as said second communication hole and as said third communication hole, and wherein of said pluralities of communication holes, ones situated on the upstream side are formed so as to have a larger diameter than the others situated on the downstream side.
 9. The rich-lean combustion burner as set forth in claim 1, wherein a plurality of communication holes are provided, in the upstream and downstream direction of said rich-side mixture introduction channel, as said first communication hole, and wherein of said plurality of communication holes, one situated on the upstream side is formed so as to have a larger diameter than the other situated on the downstream side.
 10. The rich-lean combustion burner as set forth in claim 1, wherein said first communication hole is formed in the shape of a long hole which is elongated in a direction in which said rich-side mixture introduction channel extends.
 11. A combustion apparatus equipped with a rich-lean combustion burner as set forth in any one of claims 1-10. 